Method for the conversion of hydrocarbons



Dec. 30. 1969 we. BORST, JR

METHOD FOR THE CONVERSION OF HYDROCARBONS Filed March 8, 1967 m. ohm

s um ucu v QQQE A //V l/E/V TOR.- William B. Borsf, Jr:

A TTOR/VEYS United States Patent US. Cl. 208-111 4 Claims ABSTRACT OFTHE DISCLOSURE Method for hydrodesulfurizing hydrocarbon preferablyboiling up to about 1100 F. by subjecting feed hydrocarbons to reactionwith hydrogen over hydrogenation catalyst so that the feed hydrocarbonsare at least mildly hydrocracked and substantially desulfurized. Thereactor efiluent is quenched in a unique manner using water or steamcondensate. The amount of quench is responsive to the measurement of thetemperature of the vapor stream out of the high pressure separatorimmediately following the reaction zone such that a predeterminedtemperature thereof (below 775 F.) is maintained in this vapor stream.Hydrocarbon products of reduced sulfur content are subsequentlyrecovered.

BACKGROUND OF THE INVENTION This invention relates to the conversion ofhydrocarbons. It particularly relates to the hydrogenation of relativelyhigh boiling hydrocarbons by catalytic exothermic reaction with anormally gaseous reactant. It specifically relates to a method forhydrocracking black oil hydrocarbons by improved manner of quenching thehydrocracking reaction.

It is well-known in the art that conversion reactions, in general, andhydrocracking reactions, specifically, are exothermic in nature; thatis, the reaction releases significant quantities of heat which must beselectively disposed of if the reaction is to be controlled and optimumresults are to be obtained. There have been a variety of prior artschemes proposed for such reactions, and in general, these embodyindirect heat exchange schemes wherein the heated eflluent is exchangedwith a relatively cold material such as incoming feedstock so that theefiluent temperature does not exceed a predetermined value and preheatof the feed is achieved.

It has now been found that there are other aspects for achievingeconomical thermal balance around an ex- SUMMARY OF THE INVENTIONTherefore, it is an object of this invention to provide an improvedmethod for the conversion of hydrocarbons.

It is also an object of this invention to provide a method for quenchingan exothermic conversion reaction.

It is a specific object of this invention to provide a method forhydrocracking relatively high boiling hydrocarbons in a facile andeconomical manner.

Accordingly, the method of the present invention comprises hydrocrackinga sulfur-containing hydrocarbon feedstock in a series of interdependentand interrelated sequence of steps, to wit: (a) introducing saidfeedstock at an inlet temperature from 700 F. to 800 F. into a catalyticreaction zone containing hydrocracking catalyst maintained underhydrocracking conditions including the presence of hydrogen and arelatively high pressure; (b) withdrawing from said zone an efiluentstream containing hydrocracked hydrocarbons; (c) passing said efiluent3,487,008 Patented Dec. 30, 1969 stream at a temperature exceeding about700 F. into a first separation zone under substantially the samepressure as maintained in said reaction zone under conditions sufiicientto produce a first vapor stream and a first liquid stream containinghydrocracked hydrocarbons; (d) measuring the temperature of said firstvapor stream; (e) introducing water as quench at a temperature from F.to 250 F. directly into the downstream side of said reaction zone in anamount responsive to said temperature measurement sufficient to maintaina predetermined rela tively high temperature of said first vapor stream;(f) cooling said first vapor stream from said measured temperature to atemperature from 50 F. to 150 F. by indirect heat exchange coolingmeans; (g) separating the cooled vapor stream in a second separationzone at substantially the same pressure as said first separation zoneunder conditions sufficient to provide a second vapor stream comprisinghydrogen, a second liquid stream containing hydrocracked hydrocarbons,and an aqueous stream containing quench water; (h) returning said secondvapor stream to said reaction zone; (i) recycling a portion of saidfirst liquid stream to combine with said feedstock in Step (a); and, (j)recovering hydrocracked hydrocarbons in high concentration.

Another embodiment of this invention includes the method hereinabovewherein said aqueous stream of Step (g) is returned to Step (e) asquench.

Another more particular embodiment of this invention includes thehereinabove method wherein said relatively high pressure is more than1000 p.s.i.g. and said predetermined temperature is more than 700 F. butless than about 775 F.

As previously mentioned, the present invention relates broadly to theconversion of hydrocarbons. Therefore, as used herein the termconversion is intended to include the saturation of olefinichydrocarbons, desulfurization, denitrogenation, cracking, etc. ofhydrocarbons. In short, this term includes any exothermic reaction whichoperates by reacting a normally gaseous reactant such as hydrogen withat least a portion of a suitable feedstock. Similarly, the termsconverted hydrocarbons and hydrogenated hydrocarbons are intended toinclude any hydrocarbons which have passed through the catalyticreaction zone even though such hydrocarbons, per se, were substantiallyunchanged in the reaction. Thus, a converted (or hydrogenated) productwould be one which has a reduced sulfur content, even though to aconsiderable extent the hydrocarbons have passed through the reactionzone substantially unchanged. In the illustrative embodiment of theinvention, more fully discussed hereinbelow, theterni conversion and theterm hydrogenation are used interchangeably to describe thehydrocracking of relatively high boiling hydrocarbon feedstocks withsimultaneous desulfurization of such feedstocks.

It was noted from the broad embodiment of the invention that the quenchis introduced into the downstream side of the reaction zone. This termis intended to include the introduction of quench into the lower portionof the catalyst bed, into the lower end of the reactor vessel, and/ orinto the transfer line between the reactor vessel and the nextsucceeding vessel which is normally a high pressure separator. The termexcludes a locus for quench which is into the catalyst bed whereinsignificant reaction is taking place, and excludes the introduction ofquench directly into the high pressure separator vessel. It ispreferable that the quench be introduced into the lower end of thereactor vessel below the catalyst bed to form a physical admixture withthe efiluent.

The present invention is uniquely applicable to hydrocarbon conversionmethods which may be characterized as hydrogen consuming and in which alarge excess of hydrogen gas reactant is maintained in the reactionzone,

thereby necessitating the recovery and recycle of a hydrogen-rich vaporstream in order for economy of operation to be achieved. In manyinstances, it is also desirable to recycle with the feedstock at least aportion of the normally liquid product efiluent; which recycle acts as adiluent stream and/ or is subject to further conversion in order toincrease the yield of converted products from the reaction.

The present invention is distinctly applicable to the hydrocrackingreaction which is utilized by the petroleum refining art to convertrelatively heavy carbonaceous material into lower boiling (or lowermolecular weight) hydrocarbon products such as gasoline and/or fuel oil,and the like. In other instances, the hydrocracking reaction is used forthe production of liquified petroleum gas (LPG). Hydrocracking alsoincludes the processing of heavy residual stocks commonly called blackoils. These black oils include atmospheric tower bottoms products,vacuum tower bottoms products (vacuum residuum), crude oil residuum,reduced crude oils, synthetic crude oils obtained from tar sand or oilshale, etc. Similarly, the present invention is applicable to theconversion of relatively heavy hydrocarbons such as those having initialboiling points above about 400 F. and end boiling points of about 1100F. With specific reference to the black oils, this class of relativelyheavy hydrocarbons are characterized by having at least by volumeboiling above about 1050 F. Normally, in hydrogenating such feedstocksas herein mentioned there is, in addition to the hydrocracking reaction,the desulfurization reaction which converts sulfur compounds intohydrogen sulfide and the denitrogenation reaction which convertsnitrogen compounds into ammonia.

Specific feedstocks which may be processed in accordance with thisinvention include a vacuum tower bottom product having a gravity of 7.1API at 60 F., and containing 4.1% by weight sulfur and 23.7% by weightasphaltic compounds; a reduced crude oil having a gravity of 11 API at60 F., and containing 10.1% by weight of asphaltic compounds and about5.2% by weight sulfur; and a vacuum residuum having a gravity of about8.8 API at 60 F., and containing 3.0% by weight sulfur and 4300 p.p.m.(parts per million by weight) of nitrogen, and having a 20.0% volumetricdistillation point of 1055 F. Generally, the asphaltic compounds arefound to be collodially dispersed within the black oil, and, whensubjected to elevated temperature and pressure has a tendency tofiocculate and/or polymerize, whereby the conversion thereof to morevaluable products becomes extremely diflicult.

In the processing of black oils the conversion conditions are thosewhich are sufficient for the purpose of achieving both desulfurizationand conversion of at least a portion of the feed hydrocarbons into lowerboiling (or lower molecular weight hydrocarbon products. Generally,these conversion conditions are significantly less severe than thosebeing currently commercially employed in processing similar chargestocks. For example, with respect to black oil processing, theconversion conditions include a temperature from 700 F. to 800 F. and apressure from 1000 p.s.i.g. to 3000 p.s.i.g. The temperature usually ismeasured at the inlet to the catalyst bed since the exothermic nature ofthe reaction wil produce a considerably higher effluent temperature. Forexample, the efiluent temperature, in the absence of quench, may be ashigh as 900 F. even though the inlet feed temperature was only about 725F. Hydrogen is added to the reaction zone in an amount from 1,000 to30,000 standard cubic feet per barrel, preferably, from about 2,000 to10,000 s.c.f./b. at the selected operation pressure. The liquid hourlyspace velocity (volume of hydrocarbon per hour per volume of catalyst)may be selected over a relatively broad range but, preferably, will bewithin the range from about 025 to about 2.0.

The hydrogenation reaction is carried out in the presence of a catalyst.The catalyst is characterized as comprising a metallic componentpossessing hydrogenation activity. This metallic component is generallycom= posited with a refractory inorganic oxide carrier material whichmay be of synthetic or natural origin. The precise composition andmethod of manufacturing the catalyst is not considered an essentialelement of the present invention; however, a siliceous carrier, such as88% by weight of alumina and 12% by weight of silica, or 63% by weightalumina and 67% by weight silica are generally preferred in use in thedesign to convert black oils into more valuable products. Suitablemetallic components, having hydrogenation activity, are those selectedfrom the group of metals of Groups VI-B and VIII of the Periodic Tableas indicated in the Periodic Chart of the Elements, Fisher ScientificCompany, 1953. Thus, the catalytic composite may comprise one or moremetallic components from the group consisting of molybdenum, tungsten,chromium, iron, cobalt, nickel, platinum, palladium, iridium, osmium,rhodium, ruthenium, and mixtures thereof. The concentration of thecatalytically active metallic component or components is dictated by theparticular metal chosen as well as the physical and chemicalcharacteristics of the black oil charge stock. The metallic componentsof Group VIB are generally present in an amount within the range ofabout 1.0% to about 20.0% by weight; the iron group metals in an amountfrom 0.2% to 10% by weight and, the platinum group metals are preferablypresent in an amount from 0.1% to about 5% by weight; all of which arecalculated as if the com ponents existed within the finished catalyticcomposite as the elemental metal.

The refractory inorganic oxide carrier material may comprise alumina,silica, zirconia, magnesia, titania, boria, strontia, hafnia, andmixtures of two or more including silica-alumina, alumina-silica-boriaphosphate, silica-zirconia, silica-magnesia, silica-titania,alumina-zirconia, alumina-magnesia, alumina-titania, magnesia-zirconia,titania-zirconia, magnesia-titania, silica-alumina-zirconia,silica-alumina-magnesia, silica-alumina-titania,silica-magnesia-zirconia, silica-alumina-boria, etc. It is preferred toutilize a carrier material containing at least a portion of silica andpreferably a composite of alumina and silica, with alumina being of thegreater proportion.

As previously noted, it was discovered in the practice of this inventionthat the measurement of the temperature in the first vapor stream fromthe hot separator is a particularly advantageous control point for theamount of quench necessary. It was further found that the predeterminedtemperature of this vapor stream from the high pressure separator shouldbe maintained below a temperature of about 775 F. but, preferably, aboveabout 700 F. It was found that at temperatures above about 775 F. theheavier normally liquid hydrocarbons are carried over into this vaporphase, thereby considerably contaminating the hydrogen gas stream whichsubsequently is to be recycled to the reaction zone. If a large amountof the heavier material is carried over into this vapor stream, the sizeand operating expense of condensing and thereby removing thehydrocarbons from the hydrogen gas would be significantly increased. Inaddition, it was found that the use of this vapor stream for the controlpoint permitted the complete elimination of all other heat exchangeequipment between the reactor vessel and the high pressure separator.Thus, the subsequently separated hydrogen gas is available for recycleat significantly higher pressures than would be the case for prior artschemes using indirect heat exchange means between the reactor vesseland high pressure separator. Obviously, savings in compressing cost canbe realized. In other words, the practice of this invention permits theuse of solely a direct quench stream, as herein defined, to control thisimportant temperature.

On the other hand, if the temperature of the vapor stream from the highpressure separator is below about 700 F. ammonia salts resulting fromthe conversion of nitrogenous compounds contained in the feedstock wouldtend to contaminate the normally liquid hydrocarbon phase from thebottom of the high pressure separator. If such were allowed to happen,the conventional way of removing these ammonia salts would be by Waterwashing; however, it is presently believed that if an attempt Were madeto water wash these relatively heavy converted hydrocarbons an emulsionwould be formed by the hydrocarbon and the water wash which would beextremely difficult to break. Therefore, as more fully discussedhereinbelow, the preferred embodiment of this invention teaches that thecontrol or a predetermined temperature level for the vapor streamleaving the high pressure separator should be less than 775 F. and morethan 700 F. However, depending upon the characteristics of thehydrocarbon feedstock and the conversion conditions chosen, reasonableexceptions to these temperature limitations may be utilized withsatisfactory operating results.

ILLUSTRATIVE DRAWING Other operating conditions and the preferredoperating techniques will be given in conjunction with the followingdescription of one embodiment of the invention with specific referenceto the drawing which is a diagrammatic representation of apparatus forpracticing one embodiment of the invention.

For the purpose of referring to the drawing, it will be assumed that themethod will be operated with the conversion of a reduced crude oilhaving a gravity of 166 API at 60 F., and an ASTM 65.0% volumetricdistillation temperature of 1034 F. The reduced crude feedstock containsabout 3.8% by weight sulfur, about 2,000 p.p.m. of nitrogen, about 6.5%by weight pentaneinsoluble asphaltic materials, a Conradson carbonresidue of about 8.0% by weight, and about 85 p.p.m. of metals,principally nickel and vanadium.

Now, with reference to the drawing, the reduced crude enters the methodor process system through line 1. It is admixed with makeup hydrogen ofabout 97.5 mol percent purity from an external source by line 2. It hasbeen found appropriate in some instances to add water to the reactionzone in admixture with the charge stock. When this is deemed advisable,the water is added via line 3. Normally, however, the use of water isnot necessary or desirable. The hydrogen-reduced crude oil mixture isfurther admixed with a hydrogen-rich recycle vapor stream (about 80.0mol percent hydrogen) from line 4. The total charge, after suitable heatexchange with various streams not shown, is passed through heater 5 toraise the temperature of the charge mixture to about 705 F. In thepractice of this embodiment it is preferred that the heated mixture inline 6 be further admixed with a hot (750 F.) recycle stream from line 7to produce a total reactor charge mixture of about 720 F. and a pressureof about 2,165 p.s.i.g.

The heated feedstock in admixture with hydrogen is now passed via line 6into conversion reactor 8 which contains catalyst disposed therein as afixed bed; such catalyst being a composite of 2.0% by weight nickel,16.0% by weight molybdenum on a carrier material comprising 68.0% byweight alumina, 22.0% by weight borontrifiuoride, and 10.0% by weightsilica. The hydrocarbon phase contacts the catalyst at a liquid hourlyspace velocity of about 8, based on the original reduced crude oil, orabout 2, based on the combined hydrocarbon feed.

The total conversion product effluent leaves reactor 8 via line 9 inadmixture with a hereinafter specified quench stream which had beenadded to the eflluent via line 35 at a temperature of from 50 F. to 250F., typically at about 120 F. Therefore, in line 9 there is the totalconversion product eflluent admixed with the quench stream which hadbeen added via line 35. Prior to the introduction of the quench stream,the conversion product effiuent is at a temperature of about 780 F. anda pressure of about 2,075 p.s.i.g. Sufiicient quench is added via line35 to lower the temperature of the effluent stream to less than 775 F.but, preferably, no lower than 700 F. prior to entering hot separator10. Due to pressure drop through the transfer line, primarily, thepressure within hot separator 10 is about 2,060 p.s.i.g. A first liquidstream is withdrawn from separator 10 through line 11 and a portion ofthis first liquid stream is diverted through line 7 to combine with theheated mixture in line 6 as previously mentioned. The remaining portionof the first liquid stream continues through line 11 into hot flash zone24.

A first vapor stream is removed from hot separator 10' through line 12.The temperature of this first vapor stream is measured by temperaturerecording device control (TRC) 36 which opens or closes control valve 37in accordance with the deviation of the measured temperature from apredetermined temperature (say, 745 F.) for this first vapor stream.Thus, if the measured temperature in line 12 is 760 F., TRC 36 wouldopen control valve 37 thereby increasing the flow of liquid quench inline 35 in an amount sufficient to maintain the ultimate temperature ofthe vapor stream in line 12 at its predetermined level of say, 745 F.After passing the temperature measurement point, the first vapor streampasses through condenser 13 (or any heat exchange means) whereby thetemperature is lowered to about F., with the pressure now being about2,005 p.s.i.g. again due to the pressure drop through the system.

The various streams flowing into and out of hot separator 10 may havethe following illustrative composition (exclusive of quench material):

It should be noted that the 19 mols/ hour of water in the reaction zoneeflluent is water of saturation in the recycle hydrogen gas streamand/or is water present in the fresh hydrogen added to the system bymeans of line 2 and/or water carried in with the feed hydrocarbons.

The cooled first vapor stream passes through line 14 where, preferably,it is admixed with a portion of a fourth liquid stream in line 23hereinafter described, and the resulting admixture is introduced intocold separator 15. A second vapor stream containing about 80.0 molpercent hydrogen is removed via line 16, is raised to a pressure ofabout 2,245 p.s.i.g., via compressor 17, and is introduced through line4 to combine with the feedstock and makeup hydrogen in line 11, ashereinabove described.

As pointed out in discussion presented thus far, the present inventionis based upon the concept of using water or steam condensate as thequench medium for the effluent of the hydrocracking reactor 8. Theamount of water added via line 35 is in response to the measuredtemperature of TRC 36 which controls valve 37; therefore, the

water which enters the system via line 35 is immediately turned intovapor in line 9 which passes directly out of hot separator 10 throughline 14 into cold separator 15 where it is now removed via line 34. Inaddition, if any water has been added to the feedstock via line 3 thenthis water may also be removed from the system via line 34 as indicated.Preferably, however, in the practice of this invention the water in line34 is returned through line 35 into reactor vessel 8. It is recognized,however, that the water in line 34 may be contaminated with a number ofcontaminants such as ammonia salts, entrained hydrocarbons, etc.;therefore, it may be still more preferable to introduce the water fromline 34 into a conventional water stripper column, not shown, whereinrelatively pure water is taken as an overhead product and returned tothe system via line 35 and/or 3. Of course, makeup water may be addedfrom an external source, not shown, as needed to accomplish the resultsdesired herein.

In conjunction with the material balance around hot separator 10, thevarious streams into and out of cold separator 15 may have the followingillustrative composition:

*972 mols/hour of water injection for ammonia removal. This, along wlththe 29 mols/hour of ammonia are removed via line 34.

Thus, the liquid stream (line 18) comprises hydrocarbons boiling for themost part below 650 F. (about 78 mol percent 650 F.hydrocarbons).

The first liquid stream in line 11 enters hot flash zone 24 at atemperature of about 745 F. and is at a substantially reduced pressureof from 100 p.s.i.g. to 500 p.s.i.g., typically about 220 p.s.i.g. Athird liquid stream is removed via line 27, combined with a fourthliquid stream, hereinafter described, to produce a combined majorproduct stream.

A third vapor stream is removed through line 25, is cooled and condensedto about 105 F. in condenser 26 and then passed into cold flashseparator through line 19; however, it is to be noted that the cooledthird vapor stream is, preferably, combined with a portion of secondliquid stream in line 18 from cold separator 15. The total materialentering cold flash separator 20 via line 19 is at a pressure of about200 p.s.i.g. and a temperature of about 105 F.

A fourth vapor stream comprising, for example, 97.5 mol percent propaneand lighter normally gaseous compo nents is removed from separator 20via line 21. Since this material contains a considerable quantity ofhydrogen sulfide it is generally subjected to a suitable treatingprocess prior to being vented and/or burned as flue gas. The particulareconomic aspects to be considered will dictate when the fourth vaporstream (line 21) is suitably treated to recover the small quantities ofC normally liquid hydrocarbons contained therein. A fourth liquid streamis removed from cold flash zone 20 via line 22 and a portion thereof isdiverted through line 23 to be combined with the cold first vapor streamin line 14 thereby forming the total feed stream to cold separator 15.The remaining amount of the fourth liquid stream is combined with thethird liquid stream in line 27 and passed to heater 28 and, then, vialine 29 into distillation tower 30. It is to be understood that thethird liquid stream in line 27 is combined with the unrecycled portionof the fourth liquid stream in line 22 for illustrative purposes only.For reasons peculiar to the particular operation involved, these streamsmay be separately fractionated to recover desired converted hydrocarbonstherefrom.

Distillation column 30 will be operated at conditions of temperature andpressure sufiicient to separate the desired fractions of convertedhydrocarbons. The particular operating conditions will be known to thoseskilled in the art from general knowledge and from theteachingspresented herein. However, for illustrative purposes, a gasoline boilingrange material having an end boiling point of about 380 F. is removedfrom column 30 via line 31. A middle distillate fraction (380 F' to 650F.) is also removed via line 32, and, finally, since the primary objectof this example was to maximize the production of fuel oil (650 F.+)having a sulfur concentration not greater than 1.0% by weight, aconverted hydrocarbon bottoms product is removed from fractionator 30via line 33.

Therefore, it can be seen from the above specific and illustrativeembodiment that the present invention provides a method forhydrogenating (hydrocracking) a relatively heavy hydrocarbon feedstockin a facile and economical manner. The use of a liquid stream as quench(line 35) is particularly advantageous in that it is cooled and at apressure substantially sufficient for introduction into the reactoreffluent Without significant additional high pressure pumping. The useof this stream also permits the complete elimination of heat exchangeequipment in the transfer line between reactor 8 and hot separator 10 sothat maximum pressure may be maintained through the separation steps insuch a manner that the recovered hydrogen-containing stream (line 16)may be advantageously reused in the process.

The invention claimed:

1. Method for hydrocracking a sulfur-containing hydrocarbon feedstockwhich comprises the steps of:

(a) introducing said feedstock at an inlet temperature from 700 F. to800 F. into a catalytic reaction zone containing hydrocracking catalystmaintained under hydrocracking conditions including the presence ofhydrogen and a relatively high pressure of more than 1000 p.s.i.g.;

(b) withdrawing from said zone an efiiuent stream containinghydrocracked hydrocarbons;

(c) passing said efliuent stream at a temperature exceeding 700 F. intoa first separation zone under substantially the same pressure asmaintained in said reaction zone under conditions sufficient to producea first vapor stream and a first liquid stream containing hydrocrackedhydrocarbons;

(d) measuring the temperature of said first vapor stream;

(e) introducing water as quench at a temperature from 50 F. to 250 F.directly into the downstream side of said reaction zone in an amountresponsive to said temperature measurement sufficient to maintain apredetermined relatively high temperature of more than 700 F. and lessthan 775 F. of said first vapor stream;

(f) cooling said first vapor stream from said measured temperature to atemperature from 50 F. to F. by indirect heat exchange cooling means;

(g) separating the cooled vapor stream in a second separation zone atsubstantially the same pressure as said first separation zone underconditions suflicient to provide a second vayor stream comprisinghydrogen, a second liquid stream containing hydrocracked hydrocarbons,and an. aqueous stream containing quench water;

(h) returning said second vapor stream to said reae- References Cit tionzone; (i) recycling a portion of said first liquid stream to UNITEDSTATES PATENTS combine with said feedstock in step (a); and 3,101,3808/1963 Har1l1 1 0 (j) recovering hydrocracked hydrocarbons in high con-5 3,119,765 1/ 1964 Cornell a1 centratiom 3,192,281 6/ 1965 Cornell208-112 2. Method according to claim 1 wherein said aqueous 3'28887611/1966 Hammond et a1 260672 stream of Step (g) is returned to Step (e)as quench. DELBERT E. GANTZ, P rimary Examiner 3. Method according toclaim 1 wherein said feedstock is characterized by having at least 10%boiling above 1050 F.

4. Method according to claim 1 wherein said feedstock boils within therange from 400 F. to 1100 F, 208-108;260-672 10 A. RIMENS, AssistantExaminer

